Intense Red‐Blue Luminescence Based on Superfine Control of Metal–Metal Interactions for Self‐Assembled Platinum(II) Complexes

Pathway-dependent Metallosupramolecular Polymerization Regulated by Ligand Geometry

Understanding structure/property correlations in self-assembly is a key but challenging requirement for developing functional materials. Herein, we explore the importance of ligand geometry to fine-tune photophysical properties (MMLCT vs. MLCT excited states) and self-assembly pathways in metallosupramolecular polymerization. To this end, we have designed two hydrophobic Pt(II) complexes, 1 and 2, containing a π-extended bidentate bipyridine ligand with different substitution pattern, resulting in different molecular geometries (linear vs. V-shaped). Detailed comparative studies revealed significant differences for both complexes in terms of their photophysical properties and self-assembly pathways in non-polar media. The V-shaped topology of 1 enables facile face-to-face molecular stacking with a certain curvature leading to luminescent spherical assemblies exhibiting MMLCT states and short Pt⋅⋅⋅Pt contacts via a single-step cooperative pathway. On the other hand, the higher preorganized linear topology of complex 2 induces a two-step competitive self-assembly process leading to the formation of one-dimensional supramolecular polymers with slipped packing and MLCT-originated emission. Our findings broaden the monomer scope for supramolecular polymerization and provide design guidelines for the realization of luminescent supramolecular assemblies.

Thermo-responsive emission induced by different delocalized excited-states in isomorphous Pd(ii) and Pt(ii) one-dimensional chains

The self-assembly of d8 transition metal complexes is essential for the development of optoelectronic and sensing materials with superior photofunctional properties. However, detailed insight into the electronic delocalization of excited states across multiple molecules, particularly in comparing 5d8 (Pt(ii)) and 4d8 (Pd(ii)) systems, remains ambiguous but important. In this study, we have successfully evaluated the differences in the excited-state delocalization and thermal responses of self-assembled Pt(ii) and Pd(ii) complexes. Although the complexes presented herein, K[M(CN)2(dFppy)]·H2O (M = Pt or Pd, dFppy = 2-(4,6-difluorophenyl)pyridinate), are crystallographically isomorphous with similarly short metal⋯metal contacts, only the Pt(ii) complex exhibited thermal equilibria between delocalized excited states, resulting in a drastic thermochromic luminescence with a red-shift of greater than 100 nm. In contrast, the dimeric localized emission from the Pd(ii) complex showed a significant increase in the quantum yield upon cooling, approaching almost unity.

Controlled crystallisation of porous crystals of luminescent platinum(II) complexes by electronic tuning of ancillary ligands

Porous molecular crystals (PMCs) have gained significant importance as next-generation functional porous materials. However, the selective crystallisation of the PMC phase remains a challenge. Herein, we have systematically controlled the stability of the luminescent PMC phase prepared using the luminescent Pt(II) complex [Pt(pbim)(N^O)] (pbim = 2-phenylbenzimidazolate, N^O = N-heteroaryl carboxylate) with Pt⋯Pt electronic interactions. The PMC phase formation varied significantly among the complexes depending on the heteroaryl group of the ancillary N^O ligand; the oxazolyl-bearing complex did not form a PMC phase, whereas the pyrazyl- and 5-fluoropyridyl-bearing complexes spontaneously formed a porous structure. This difference was rationalised by the π-stacking capability of the heteroaryl group of the ancillary ligand. Furthermore, owing to the presence of the one-dimensional Pt⋯Pt chains in this PMC phase, the photophysical properties of PMCs resulting from the Pt⋯Pt interactions were also significantly changed by the ancillary ligands.

Influence of O-H⋅⋅⋅Pt interactions on photoluminescent response in the (Et4N)2{[Pt(bph)(CN)2][phenylene-1,4-diresorcinol]} framework

Tunable photoluminescence (PL) is one of the hot topics in current materials science, and research performed on the molecular phases is at the forefront of this field. We present the new (Et4N)2[PtII(bph)(CN)2]⋅rez3⋅1/3H2O (Pt2rez3) (bph=biphenyl-2,2'-diyl; rez3=3,3",5,5"-tetrahydroxy-1,1':4',1"-terphenyl, phenylene-1,4-diresorcinol coformer, a linear quaternary hydrogen bond donor) co-crystal salt based on the recently appointed promising [PtII(bph)(CN)2]2- luminophore. Within the extended hydrogen-bonded subnetwork [PtII(bph)(CN)2]2- complexes and rez3 coformer molecules form two types of contacts: the rez3O-H⋅⋅⋅Ncomplex ones in the equatorial plane of the complex and non-typical rez3O-H⋅⋅⋅Pt ones along its axial direction. The combined structural, PL, and DFT approach identified the rez3O-H⋅⋅⋅Pt synthons to be crucial in promoting the noticeable uniform redshift of bph ligand centered (LC) emission compared to the LC emission of the (Et4N)2[PtII(bph)(CN)2]⋅H2O (Pt2) precursor, owing to the direct interference of the phenol group with the PtII-bph orbital system via altering the CT processes within. The high-resolution emission spectra for Pt2 and Pt2rez3 were successfully reproduced at 77 K by using the Franck-Cordon expressions. The possibility to tune PL properties along the plausible continuum of rez3O-H⋅⋅⋅Pt synthons is indicated, considering various scenarios of molecular occupation of the space above and below the complex plane.

Chromic soft crystals based on luminescent platinum(II) complexes

Platinum(II) complexes of square-planar geometry are interesting from a crystal engineering viewpoint because they exhibit strong luminescence based on the self-assembly of molecular units. The luminescence color changes in response to gentle stimuli, such as vapor exposure or weak mechanical forces. Both the molecular and the crystal designs for soft crystals are critical to effectively generate the chromic luminescence phenomenon of Pt(II) complexes. In this topical review, strategies for fabricating chromic luminescent Pt(II) complexes are described from a crystal design perspective, focusing on the structural regulation of Pt(II) complexes that exhibit assembly-induced luminescence via metal-metal interactions and structural control of anionic Pt(II) complexes using cations. The research progress on the evolution of various chromic luminescence properties of Pt(II) complexes, including the studies conducted by our group, are presented here along with the latest research outcomes, and an overview of the frontiers and future potential of this research field is provided.

Chromic and dynamic: soft crystals of platinum(II) complexes pave the way for multi-responsive materials

The development of smart, stimuli-responsive materials has received increased attention in the past decade for their applications as sensing technologies. This commentary discusses a timely topical review by Kato [(2024). IUCrJ, 11, 442-452] on the fabrication of multi-stimuli responsive crystals comprised of luminescent platinum(II) complexes, which exhibit intriguing chromic phenomena in response to stimuli.

Precise Regulation the Multiemission Based on Soft Double Salt for Information Encryption

Manipulation of multiemissive luminophores is meaningful for exploring luminescent materials. Herein, we report a soft double salt assembly strategy that could result in well-organized nanostructures and different luminescence based on multiple weak intermolecular interactions thanks to the existence of electrostatic attraction between the anionic and cationic platinum(II) complexes. The cationic complexes B1 and B2 can coassemble with anionic complex A, respectively, and the emission switches from monomeric and excimeric emission to the triplet metal-metal-to-ligand charge transfer (3MMLCT) along with morphology changes from 0-dimensional (0-D) nanospheres to 3-dimensional (3-D) nanostructures. It is demonstrated that an isodesmic growth mechanism is adopted during the spontaneous self-assembly process, and the relative negative ΔG values make the anionic and cationic complex molecules prefer to form aggregates based on π-π stacking, Pt···Pt interactions, and electrostatic interactions. The coassembly strategy between anionic and cationic complexes endows them with multicolor luminescent and apparent color as optical materials for advanced information encryption.

Photoluminescence of Platinum(II) Complexes with Diazine-Based Ligands

In the last past twenty years, research on luminescent platinum (II) complexes has been intensively developed for useful application such as organic light emitting diodes (OLEDs). More recently, new photoluminescent complexes based on diazine ligands (pyrimidine, pyrazine, pyridazine, quinazoline and quinoxaline) have been developed in this context. This review will summarize the photophysical properties of most of the phosphorescent diazine Pt(II) complexes described in the literature and compare the results to pyridine analogues whenever possible. Based on the emission color, and the photoluminescence quantum yield (PLQY) values, the relationship between structure modification, and photophysical properties are highlighted. Tuning of emission color, quantum yields in solution and solid state and, for some complexes, aggregation induced emission (AIE) or thermally activated delayed fluorescence (TADF) properties are described. When emitting OLEDs have been built from diazine Pt(II) complexes, the external quantum efficiency (EQE) values and luminance for different emission wavelengths and in some cases, chromaticity coordinates obtained from devices, are given. Finally, this review highlights the growing interest in studies of new luminescent diazine Pt(II) complexes for OLED applications.

Dual Enhancement of Phosphorescence and Circularly Polarized Luminescence through Entropically Driven Self-Assembly of a Platinum(II) Complex

Addressing the dual enhancement of circular polarization (glum) and luminescence quantum yield (QY) in circularly polarized luminescence (CPL) systems poses a significant challenge. In this study, we present an innovative strategy utilizing the entropically driven self-assembly of amphiphilic phosphorescent platinum(II) complexes (L-Pt) with tetraethylene glycol chains, resulting in unique temperature dependencies. The entropically driven self-assembly of L-Pt leads to a synergistic improvement in phosphorescence emission efficiency (QY was amplified from 15 % at 25 °C to 53 % at 60 °C) and chirality, both in the ground state and the excited state (glum value has been magnified from 0.04×10-2 to 0.06) with increasing temperature. Notably, we observed reversible modulation of phosphorescence and chirality observed over at least 10 cycles through successive heating and cooling, highlighting the intelligent control of luminescence and chiroptical properties by regulating intermolecular interactions among neighboring L-Pt molecules. Importantly, the QY and glum of the L-Pt assembly in solid state were measured as 69 % and 0.16 respectively, representing relatively high values compared to most self-assembled CPL systems. This study marks the pioneering demonstration of dual thermo-enhancement of phosphorescence and CPL and provides valuable insights into the thermal effects on high-temperature and switchable CPL materials.

Reblooming of the cis-Bis(2-phenylpyridine) Platinum(II) Complex: Synthesis Updating, Aggregation-Induced Emission, Electroluminescence, and Cell Imaging

Studies on the syntheses, photophysical properties, and applications of cis-bis(2-phenylpyridine) platinum(II) complex (Pt(ppy)2) family are of great importance, but very limited progress has been achieved to date. Herein, a one-pot method was established for the syntheses of Pt(ppy)2-type complexes Pt-ppy and Pt-tBu. These two compounds were nonemissive in dilute solutions. However, they produced intense red and deep-red phosphorescence in the aggregation and film states, with lifetimes and quantum yields up to 1.92 μs and 70%, respectively, exhibiting unique aggregation-induced emission (AIE) characteristics. According to the experimental and theoretical studies, molecular configuration transformation (MCT) in the excited state may occur because of the d-d transition from the Pt center, causing nonradiative transitions in the solution. Nevertheless, the MCT would be largely restricted by the intermolecular interactions or rigid matrix, thereby enabling efficient phosphorescence in the aggregation state and in the PMMA films. Consequently, the AIE characteristics of Pt-ppy and Pt-tBu probably result from the restriction of molecular configuration transformation (RMCT). Due to the π-π and/or weak Pt-Pt interactions and the concentration-dependent emission characteristics, they emit deep-red and NIR emissions generated by excimer and/or MMLCT emitting species. Inspired by their AIE features, electroluminescence and cell imaging applications are explored. To the best of our knowledge, this is the first comprehensive study on the synthesis optimization, photophysical properties, AIE characteristics, and applications of the Pt(ppy)2-type complexes, which may rebloom the research studies on this type of Pt(II) complex family and provide valuable insights on the development of phosphorescent AIE metal-organic complexes.

Nickel(II) Analogues of Phosphorescent Platinum(II) Complexes with Picosecond Excited-State Decay

Square-planar NiII complexes are interesting as cheaper and more sustainable alternatives to PtII luminophores widely used in lighting and photocatalysis. We investigated the excited-state behavior of two NiII complexes, which are isostructural with two luminescent PtII complexes. The initially excited singlet metal-to-ligand charge transfer (1 MLCT) excited states in the NiII complexes decay to metal-centered (3 MC) excited states within less than 1 picosecond, followed by non-radiative relaxation of the 3 MC states to the electronic ground state within 9-21 ps. This contrasts with the population of an emissive triplet ligand-centered (3 LC) excited state upon excitation of the PtII analogues. Structural distortions of the NiII complexes are responsible for this discrepant behavior and lead to dark 3 MC states far lower in energy than the luminescent 3 LC states of PtII compounds. Our findings suggest that if these structural distortions could be restricted by more rigid coordination environments and stronger ligand fields, the excited-state relaxation in four-coordinate NiII complexes could be decelerated such that luminescent 3 LC or 3 MLCT excited states become accessible. These insights are relevant to make NiII fit for photophysical and photochemical applications that relied on PtII until now.

Vapor-Induced Assembly of a Platinum(II) Complex Loaded on Layered Double Hydroxide Nanoparticles

Controlled self-assembly of PtII complexes is key to the development of optical and stimuli-responsive materials, but designing and precisely controlling them is still difficult owing to weak intermolecular interactions. Herein, we report the successful water-vapor-induced assembly of an anionic PtII complex [Pt(CN)2 (ppy)]- (Hppy=2-phenylpyridine) electrostatically loaded onto cationically charged layered double hydroxide (LDH) nanoparticles consisting of Mg2+ and Al3+ ions. When the PtII complexes were densely loaded onto the LDH nanoparticles, the assembly was maintained, even in dilute aqueous media. In the case of sparse loading, the PtII complexes were loaded discretely in the dry state; however, when water vapor was adsorbed, the increased mobility of the PtII complexes led to their assembly on the LDH nanoparticles. The presence of water vapor led to a drastic change in luminescence from green to orange.

Metalation of a Hierarchical Self-Assembly Consisting of π-Stacked Cubes through Single-Crystal-to-Single-Crystal Transformation

Single-crystal-to-single-crystal metalation of organic ligands represents a novel method to prepare metal-organic complexes, but remains challenging. Herein, a hierarchical self-assembly {(H₁₂L₈)·([N(C₂H₅)₄]⁺)₃·(ClO₄^-)₁₅·(H₂O)₃₂} (1) (L = tris(2-benzimidazolylmethyl) amine) consisting of π-stacked cubes which are assembled from eight partially protonated L ligands is obtained. By soaking the crystals of compound 1 in the aqueous solution of Co(SCN)₂, the ligands coordinate with Co²⁺ ions stoichiometrically and ClO₄^- exchange with SCN^- via single-crystal-to-single-crystal transformation, leading to {([CoSCNL]⁺)₈·([NC₈H₂₀]⁺)₃·(SCN)₁₁·(H₂O)₁₃} (2).

Chromic triboluminescence of self-assembled platinum(II) complexes

A series of Pt(II) complexes bearing N-heterocyclic carbenes, [Pt(CN)₂(Rim-Mepy)] (Rim-MepyH⁺ = 3-alkyl-1-(4-methyl-(2-pyridinyl))-1H-imidazolium, R = Me, Et, ⁱPr, or ^tBu), exhibits triboluminescence in the visible range from blue to red, as well as the corresponding intense photoluminescence. Remarkably, among the complexes, the ⁱPr-substituted one exhibits chromic triboluminescence behaviour during the process of rubbing and also vapour exposure.

Elastic and bright assembly-induced luminescent crystals of platinum(II) complexes with near-unity emission quantum yield

Molecular crystals of Pt(II) complexes with metallophilic interactions can provide bright assembly-induced luminescence with colour tunability. However, the brittleness of many of these crystals makes their application in flexible optical materials difficult. Herein, we have achieved the elastic deformation of crystals of polyhalogenated Pt(II) complexes exhibiting bright assembly-induced luminescence. A crystal of [Pt(bpic)(dFppy)] (Hbpic = 5-bromopicolinic acid, HdFppy = 2-(2,4-difluorophenyl)pyridine) and a co-crystal of [Pt(bpic)(dFppy)] and [Pt(bpic)(ppy)] (Hppy = 2-phenylpyridine) were found to exhibit significant elastic deformation due to their highly anisotropic interaction topologies. While the crystal of [Pt(bpic)(dFppy)] exhibited monomer-based ligand-centred ³ππ* emission with an emission quantum yield of 0.40, the co-crystal exhibited bright, triplet metal-metal-to-ligand charge transfer (³MMLCT) emission owing to Pt⋯Pt interactions, thereby achieving a significantly higher emission quantum yield of 0.94.

A Preinstalled Protic Cation as a Switch for Superprotonic Conduction in a Metal-Organic Framework

Metal-organic frameworks (MOFs), made from various metal nodes and organic linkers, provide diverse research platforms for proton conduction. Here, we report on the superprotonic conduction of a Pt dimer based MOF, [Pt₂(MPC)₄Cl₂Co(DMA)(HDMA)·guest] (H₂MPC, 6-mercaptopyridine-3-carboxylic acid; DMA, dimethylamine). In this framework, a protic dimethylammonium cation (HDMA⁺) is trapped inside a pore through hydrogen bonding with an MPC ligand. Proton conductivity and X-ray measurements revealed that trapped HDMA⁺ works as a preinstalled switch, where HDMA⁺ changes its relative position and forms an effective proton-conducting pathway upon hydration, resulting in more than 10⁵ times higher proton conductivity in comparison to that of the dehydrated form. Moreover, the anisotropy of single-crystal proton conductivity reveals the proton-conducting direction within the crystal. The present results offer insights into functional materials having a strong coupling of molecular dynamic motion and transport properties.

Phosphorescent Cyclometalated Platinum(II) Enantiomers with Circularly Polarized Luminescence Properties and Their Assembly Behaviors

Platinum(II) complexes as supramolecular luminescent materials have received considerable attention due to their unique planar structures and fascinating photophysical properties. However, the molecular design of platinum(II) complexes with impressive circularly polarized luminescence properties still remains challenging and rarely explored. Herein, we reported a series of cyclometalated platinum(II) complexes with benzaldehyde and its derived imine-containing alkynyl ligands to investigate their phosphorescent, chiroptical, and self-assembly behaviors. An isodesmic growth mechanism is found for their temperature-dependent self-assembly process. The chiral sense of the enantiomers can be transferred from the chiral alkynyl ligands to the cyclometalated platinum(II) dipyridylbenzene N^C^N chromophore and further amplified through supramolecular assembly via intermolecular noncovalent interactions. Notably, distinctive phosphorescent properties and nanostructured morphologies have been found for enantiomers 4R and 4S. Their intriguing self-assembled nanostructures and phosphorescence behaviors are supported by crystal structure determination, ¹H NMR, emission, and UV-vis absorption spectroscopy, scanning electron microscopy, and X-ray powder diffraction studies.

Metal-Metal-to-Ligand Charge Transfer in Pt(II) Dimers Bridged by Pyridyl and Quinoline Thiols

The investigation of two distinct species of square planar dinuclear Pt(II) dimers based on anti-[Pt(C^∧N)(μ-N^∧S)]₂, where C^∧N is either 2-phenylpyridine (ppy) or benzo(h)quinoline (bzq) and N^∧S is pyridine-2-thiol (pyt), 6-methylpyridine-2-thiol (Mpyt), or 2-quinolinethiol (2QT), is presented. Each molecule was thoroughly characterized with electronic structure calculations, static UV-vis and photoluminescence (PL) spectroscopy, and cyclic voltammetry, along with transient absorbance and time-gated PL experiments. These visible absorbing chromophores feature metal-metal-to-ligand charge-transfer (MMLCT) excited states that originate from intramolecular d⁸-d⁸ metal-metal σ-interactions and are manifested in the ground- and excited-state properties of these molecules. All five molecules reported (anti-[Pt(ppy)(μ-Mpyt)]₂ could not be isolated), three of which are newly conceived here, possess electronic absorptions past 500 nm and high quantum yield PL emission with spectra extending into the far red (λ_em > 700 nm), originating from the charge-transfer state in each instance. Each chromophore displays excited-state decay kinetics adequately modeled by single exponentials as recorded using dynamic absorption and PL experiments; each technique yields similar decay kinetics. The combined data illustrate that pyridyl and quinoline-thiolates in conjunction with select cyclometalates represent classes of MMLCT chromophores that exhibit excited-state properties suitable for promoting light-energized chemical reactions and provide a molecular platform suitable for evaluating coherence phenomena in transient metal-metal bond-forming photochemistry.

Solid-State Structures and Photoluminescence of Lamellar Architectures of Cu(I) and Ag(I) Paddlewheel Clusters with Hydrogen-Bonded Polar Guests

Two hexanuclear paddlewheel-like clusters appending six carboxylic-acid pendants have been isolated with the inclusion of polar solvent guests: [Cu₆(Hmna)₆]·7DMF (1·7DMF) and [Ag₆(Hmna)₆]·8DMSO (2·8DMSO), where H₂mna = 2-mercaptonicotininc acid, DMF = N,N’-dimethylformamide, and DMSO = dimethyl sulfoxide. The solvated clusters, together with their fully desolvated forms 1 and 2, have been characterized by FTIR, UV–Vis diffuse reflectance spectroscopy, TG-DTA analysis, and DFT calculations. Crystal structures of two solvated clusters 1·7DMF and 2·8DMSO have been unambiguously determined by single-crystal X-ray diffraction analysis. Six carboxylic groups appended on the clusters trap solvent guests, DMF or DMSO, through H-bonds. As a result, alternately stacked lamellar architectures comprising of a paddlewheel cluster layer and H-bonded solvent layer are formed. Upon UV illumination (λ_ex = 365 nm), the solvated hexasilver(I) cluster 2·8DMSO gives intense greenish-yellow photoluminescence in the solid state (λ_PL = 545 nm, Φ_PL = 0.17 at 298 K), whereas the solvated hexacopper(I) cluster 1·7DMF displays PL in the near-IR region (λ_PL = 765 nm, Φ_PL = 0.38 at 298 K). Upon complete desolvation, a substantial bleach in the PL intensity (Φ_PL < 0.01) is observed. The desorption–sorption response was studied by the solid-state PL spectroscopy. Non-covalent interactions in the crystal including intermolecular H-bonds, CH⋯π interactions, and π⋯π stack were found to play decisive roles in the creation of the lamellar architectures, small-molecule trap-and-release behavior, and guest-induced luminescence enhancement.

Reversible On-Off Switching of Excitation-Wavelength-Dependent Emission of a Phosphorescent Soft Salt Based on Platinum(II) Complexes

Excitation-wavelength-dependent (Ex-De) emission materials show excellent potential in diverse advanced photonic areas. Of significant importance is the on-demand regulation of the Ex-De luminescence behavior of these materials, which is previously unprecedented. In this study, we report on a platinum(II) complex-based phosphorescent soft salt S1 ([Pt(tpp)(ed)]⁺[Pt(ftpp)(CN)₂]^- (where ttp = 2-(4-(trifluoromethyl)phenyl)pyridine, ed = ethane-1,2-diamine, and ftpp = 2-(4-fluoro-3-(trifluoromethyl)phenyl)pyridine)) with Ex-De photoluminescence (PL) property. UV-visible absorption and PL spectra of S1 were recorded in DMSO-H₂O mixture (1 × 10^-3 M) with various H₂O fractions to investigate its ground and excited states. Interestingly, the PL spectra of S1 powder show that its maximum emission peak is red-shifted from 595 to 644 nm upon excitation at different wavelengths from 360 to 520 nm, accompanied by an obvious emission color change from yellow-orange to red. Furthermore, confocal laser scanning fluorescence microscopy was employed to determine the PL property of self-assembled uniform S1 nanostructure, and the result shows that the Ex-De emission behavior is absent. On the basis of these results, we conclude the various Pt(II)···Pt(II) distances that exist are the major factor responsible for the properties of the Ex-De PL of S1 powder. Thus, for the first time, reversible on-off switching of Ex-De PL of S1 was achieved by manipulating its Pt(II)···Pt(II) distances through mechanical stress and vapor fuming. Finally, we demonstrate the high-level anticounterfeiting applications via on-demand multicolor displays.

Origin of the Aggregation-Induced Phosphorescence of Platinum(II) Complexes: The Role of Metal-Metal Interactions on Emission Decay in the Crystalline State

Discerning the origins of the phosphorescent aggregation-induced emission (AIE) from Pt(II) complexes is crucial for developing the broader range of photo-functional materials. Over the past few decades, several mechanisms of phosphorescent AIE have been proposed, however, not have been directly elucidated. Herein, we describe phosphorescence and deactivation processes of four class of AIE active Pt(II) complexes in the crystalline state based on experimental and theoretical investigation. These complexes show metal-to-ligand and/or metal-metal-to-ligand charge transfer emission in crystalline state with different heat resistance against thermal emission quenching. The calculated energy profiles including the minimum energy crossing point between S₀ and T₁ states were consistent with the heat resistant properties, which provided the mechanism for AIE expression. Furthermore, we have clarified the role of metal-metal interaction in AIE by comparing two computational models.

Chameleonic Photo- and Mechanoluminescence in Pyrazolate-Bridged NHC Cyclometalated Platinum Complexes

DFT investigations on the ground (GS) and the first triplet (T₁) excited state potential energy surfaces (PES) were performed on a new series of platinum-butterfly complexes, [{Pt(C^∧C*)(μ-Rpz)}₂] (Rpz: pz, 1; 4-Mepz, 2; 3,5-dmpz, 3; 3,5-dppz, 4), containing a cyclometalated NHC in their wings. The geometries of two close-lying local minima corresponding to butterfly spread conformers, 1s-4s, and butterfly folded ones, 1f-4f, with long and short Pt-Pt separations, respectively, were optimized in the GS and T₁ PES. A comparison of the GS and T₁ energy profiles revealed that an opposite trend is obtained in the relative stability of folded and spread conformers, the latter being more stabilized in their GS. Small ΔG (s/f) along with small-energy barriers in the GS support the coexistence of both kinds of conformers, which influence the photo- and mechanoluminescence of these complexes. In 5 wt % doped PMMA films in the air, these complexes exhibit intense sky-blue emissions (PLQY: 72.0-85.9%) upon excitation at λ ≤ 380 nm arising from ³IL/MLCT excited states, corresponding to the predominant 1s-4s conformers. Upon excitation at longer wavelengths (up to 450 nm), the minor 1f-4f conformers afford a blue emission as well, with PLQY still significant (40%-60%). In the solid state, the as-prepared powder of 4 exhibits a greenish-blue emission with QY ∼ 29%, mainly due to ³IL/³MLCT excited states of butterfly spread molecules, 4s. Mechanical grinding resulted in an enhanced and yellowish-green emission (QY ∼ 51%) due to the ³MMLCT excited states of butterfly folded molecules, 4f, in such a way that the mechanoluminescence has been associated with an intramolecular structural change induced by mechanical grinding.

The Observation of Interchain Motion in Self-Assembled Crystalline Platinum(II) Complexes: An Exquisite Case but By No Means the Only One in Molecular Solids

In organic and organometallic solids, upon electronic excitation, most intermolecular structural relaxations follow a pathway along the π-π stacking direction or metal-metal bond with significant coupling strength. Differently, we discovered that the self-assembled platinum(II) complexes, Pt(fppz)₂, exhibit an unusual interchain contraction. The ground-state and excited-state multiple local minima were distinguished by temperature-dependent excitation/emission spectra, indicating the existence of multiple local minima. The time-resolved emission decay revealed the excited-state structural relaxation lifetime with τ_obs = 41 ns at 298 K. Temperature-dependent X-ray diffraction analysis showed that the packing geometries contract 0.6 Å along the interchain direction (a-axis) at 50 K compared to the geometries at 298 K. Such structural displacements render the slow internal conversion rate in the excited states. We thus demonstrate the correlation between the packing geometries and the excited-state dynamics of the self-assembled Pt(II) complexes, shedding light on the unique direction of interchain structural deformation of the molecular aggregates.

Trinuclear Organometallic Pt-Ir-Pt Complexes: Insights into Photophysical Properties, Amino Acid Binding and Protein Sensing

The rational synthesis of trinuclear emissive organometallic complexes with two equivalent platinum(II) centres appended to the ancillary substituted 2,2'-bipyridyl ligand of the cyclometalated iridium(III) centre is reported here. The alkynyl-platinum moiety and cyclometalated iridium(III) centres have been separated through a non-conjugated CH₂ -O-CH₂ linkage. The emission titration with amino acids reveals that the complexes sense free amino acids. The luminescence sensing of BSA is thus attributed to the amino acid sensing ability of the complexes and confirmed by emission anisotropy and Far-UV CD spectral study. The decrease in α-helix in the CD spectra signifies the changes in the secondary structure of protein in presence of the complexes.

Controllable synthesis of two adenosine 5'-monophosphate nucleotide coordination polymers via pH regulation: crystal structure and chirality

Two types of Cu(ii)-AMP-4,4'-bipy coordination polymers, {[Cu(AMP)(4,4'-bipy)(H₂O)₃]·5H₂O}n (1) and {[Cu₂(HAMP)₂(4,4'-bipy)₂(H₂O)₄]·2NO₃·11H₂O}n (2) (Na₂AMP = adenosine 5'-monophosphate disodium salt), were synthesised through pH control. X-ray single-crystal diffraction analysis revealed that 1 and 2 are one-dimensional (1D) coordinating coordination polymers. The nucleotide in 1 was not protonated whereas that in 2 was protonated. With the protonated NO₃^- in 2 entering the crystal lattice, it plays a role in balancing the charge. The chirality was studied using solid-state circular dichroism (CD) spectroscopy based on the analysis of crystal structures.

Strategy for Achieving Long-Wavelength Near-Infrared Luminescence of Diimineplatinum(II) Complexes

Although many strategies have been used to help design effective near-infrared (NIR) luminescent materials, it is still a huge challenge to realize long-wavelength NIR luminescence of diimineplatinum(II) complexes in the solid state. Herein, we have successfully achieved long-wavelength NIR luminescence of a family of diimineplatinum(II) complexes based on a new strategy that combines a one-dimensional (1D) "Pt wire" structure with the electronic effect of the substituent. The structures of six solvated diimineplatinum(II) complexes based on 4,4-dichloro-2,2'-bipyridine or 4,4-dibromo-2,2'-bipyridine and 4-substituted phenylacetylene ligands have been determined, namely, 1·¹/₂toluene, 2·¹/₂THF, 3·¹/₈toluene, 4·¹/₂THF, 5·¹/₈CH₂Cl₂, and 6·¹/₄toluene. All of them crystallize in the monoclinic space group C2/c or C2/m and stack in the 1D "Pt wire" structure. In the solid state, six complexes exhibited unusual long-wavelength metal-metal-to-ligand charge-transfer luminescence that peaked at 984, 1044, 972, 990, 1022, and 935 nm, respectively. Interestingly, 2·¹/₂THF has the shortest Pt···Pt distance and the longest emission wavelength among the six complexes. As far as we know, the luminescence of 2·¹/₂THF at 1044 nm is the longest emission wavelength among known diimineplatinum(II) complexes. Systematic studies revealed that good molecular planarity, suitable substituent position, weak hydrogen-bond-forming ability of the substituents, appropriate molecular bending, and weakening of the interaction between solvated molecules and platinum molecules are conducive to the construction of a 1D "Pt wire" structure of the diimineplatinum(II) complex. Furthermore, the emission energy of the complex is mainly determined by the strength of the Pt-Pt interaction and electronic effect of the substituent.

Luminescent terpyridine appended geminal bisazide and bistriazoles: multinuclear Pt(II) complexes and AIPE-based DNA detection with the naked eye

We report square planar Pt(ii) complexes as luminescent biosensors for DNA detection in solution. The sensing is attributed to the aggregation induced bright red photoluminescence (AIPE) of the complexes in the presence of DNA that can be seen with the naked eye using only a 360 nm light source. Terpyridine appended luminescent geminal bistriazoles (L1-L4, from geminal bisazide A through azide-alkyne 'click' cycloaddition) with versatile chelating sites were explored for metal coordination and reaction with Pt(dmso)2Cl2 yielding tetranuclear and dinuclear complexes of Pt(ii) with different N∩N ligand environments. Thermally stable gem-bisazide and bistriazoles are hardly reported in the literature and this is the first report of terpyridine appended geminal bisazide and bistriazoles.

Long-wavelength NIR luminescence of 2,2′-bipyridyl-Pt(ii) dimers achieved by enhanced Pt–Pt interaction

Benefiting from the very strong intermolecular Pt–Pt interaction, 2,2′-bipyridyl-Pt(ii) dimers have achieved long-wavelength near-infrared luminescence exceeding 1000 nm for the first time.